1. Field
The present disclosure generally relates to testing methods and, in particular, testing a tubular member simultaneously in bending and torsion.
2. Description of the Related Art
Thin-walled tubular structural members are sometimes used in applications where the member is subjected to combined bending and torsional loads. For example, tubular members may be used as part of the structure of a wing or tail of an aircraft. It is often desirable to test the performance of these structural members to determine their true capabilities and thereby increase the confidence in the design.
Current methods of performing bending and torsional tests of thin-walled tubular members present a number of difficulties. Bending tests are commonly performed by the application of a lateral load to the midpoint of the tubular member. For very thin-walled tubes, performing a bending test alone can be problematic due to the tendency of any test fixture restraint to crush or damage the tube wall. In addition, one failure mode of a bending test is a buckling failure in the exact region where the lateral load is applied, raising the potential that the test fixture will interfere with the failure mode. In these cases, an edgewise compression test is sometimes used as a compromise approach, but this type of test may not capture the true bending and buckling stability capability of the tubular member.
If a torsional load is applied at the same time as the lateral load, the portion of the fixture that is applying the lateral load may induce an inadvertent torsional restraint in the test. The local stresses created by the application of the side load and the inadvertent torsional restraint at the midpoint may result in a failure at the midpoint due to stress conditions that are not representative of the true condition in service.
To avoid the problems and uncertainties related to performing a combined bending and torsion test of a thin-walled tubular member, bending and torsion tests are often performed separately and combined by analytical means, which introduces uncertainties that may preclude achieving minimum weight structure.